1. Field of the Invention
The present invention relates in general to a marine propulsion system, and in particular to a transmission system for a counter-rotational propulsion device.
2. Description of Related Art
Many outboard drives of marine watercrafts employ counter-rotational propeller systems which utilize a pair of counter-rotating propellers that operate in series about a common rotational axis. By using propeller blades having a pitch of opposite hands, the dual propeller arrangement provides significant improvement in propulsion efficiency. Such transmissions are common in both outboard motors and in outboard drive units of inboard/outboard motors.
Prior designs of counter-rotational propeller systems, however, are not easily or readily incorporated into existing single propeller outboard drives because of incompatibilities between the components of the old drive units and the counter-rotational propulsion systems. As such, the conversion process usually is not cost efficient. This new propulsion technology thus has generally not been integrated into existing outboard drives.
In addition, prior designs of counter-rotational propulsion systems tend to operate inefficiently when driven in reverse. In prior counter-rotational propulsion system designs, the propulsion system drives both propellers in opposite directions during a forward drive mode, and drives only a rear propeller during a reverse drive mode. The front propeller, however, tends to block the thrust stream produced by the rear propeller and thereby inhibits the performance of the outboard drive when operated in reverse.